Organic materials and especially polymers have proven to be difficult organic materials to stabilize against the deleterious affects of oxygen and ozone, particularly the unsaturated polymers, both natural and synthetic. Although many materials have been suggested and used as stabilizers in oxidizable organic materials, no completely satisfactory material has been found that will fully protect these materials under the widely different conditions to which they are subjected.
Phenolic compounds have been among the more commonly used compounds that have found wide scale acceptance as polymer stabilizers. However, many of the phenolic antioxidants, although reasonably effective stabilizers for organic materials, tend to impart discoloration and staining to the materials they are intended to stabilize and further have exhibited limited utility when used in compositions that are subjected to extreme oxidative or degradative conditions.
Further, some of the previously known phenolic antioxidants have limited solubility in certain materials. This insolubility has caused difficulties in the incorporation of the antioxidant and also results in the antioxidant's migration from the material to be protected.
Synergists have been used and developed over the years as a method for enhancing the ability of a phenolic compound to prevent the oxidative degradation of the organic material. The synergists are commonly sulfur containing compounds that enhance the ability of the antioxidant to protect the substrate from oxidative degradation.
There is presently a need in the industry for a low-cost material that will provide excellent protection to oxidizable organic materials yet be easily prepared from readily available and inexpensive raw materials. The instant invention provides a material that is both low in cost and easily prepared while also providing excellent stability to the materials in which it is incorporated.
U.S. Pat. No. 2,417,118 discloses a Mannich base catalyzed process for the preparation of a mono-nuclear phenolic motor fuel additive which comprises reacting an aromatic compound containing at least one hydroxyl radical with formaldehyde and an alkyl mercaptan. However, U.S. Pat. No. 2,417,118 does not suggest the use of an acid catalyst nor the use of an azeotroping solvent. Further, U.S. Pat. No. '118 does not suggest the molar ratios of the reactants which are disclosed and claimed in the instant application or the fact that the reaction product of the instant invention has outstanding properties for the stabilization of rubbers.
U.S. Pat. No. 3,260,758 discloses the base catalyzed preparation of 2,6 or 2,4 dialkyl 4 or 6 alkylthiomethyl phenols. U.S. Pat. No. '758 states that the process disclosed in U.S. Pat. No. 2,417,118 is plagued by long reaction times, the formation of color bodies and the side reaction product of methylene bis phenols. U.S. Pat. No. '758 produces a singular mono-nuclear phenolic product through the use of a 2,4 or 2,6 disubstituted alkyl phenolic starting material. U.S. Pat. No. '758 also uses only strong bases as catalysts for the reaction, and does not suggest or limit molar ratios of reactants nor does it suggest that toluene should be used as an azeotroping solvent.
U.S. Pat. No. 3,462,392 deals with the stabilization of polyolefins using a specific combination of dinonylphenol and methylene bis-dinonylphenol as a stabilizer. This patent suggests the preparation of the bis compound through an acid catalyzed reaction of formaldehyde with a 2,4 disubstituted phenol.
U.S. Pat. No. 3,553,270 describes the reaction of phenols unsubstituted in at least one position ortho or para to the hydroxyl group with formaldehyde and mono or dimercaptans to yield .alpha.-(hydro-carbylthio)-cresols or .alpha.,.alpha.-alkylene dithiobis compounds. This patent mentions the method of U.S. Pat. Nos. 2,322,376 and 2,417,118 and states that the direct reaction between a phenol, formaldehyde and a mercaptan is operable on 2,6 dialkylphenols only with an alkaline catalyst and that it tends to give colored products and, especially with the less hindered 2,6 dialkylphenols is complicated by a side reaction leading to a methylenebisphenol. The process of U.S. Pat. No. 3,553,270 for preparing .alpha.-(hydro-carbylthio)-cresols avoids the problems of methylene bis phenols production through the use of a 2,6 or 2,4 disubstituted phenols as starting materials. The U.S. Pat. No. '270 patent does not suggest and even teaches away from the instant discovery that use of alkylated phenols in an acid catalyzed reaction with formaldehyde and a mercaptan under azeotroping conditions will produce highly effective stabilizers for oxidizable organic materials.
U.S. Pat. No. 4,358,616 claims a process for the preparation of alkylthiomethylphenols which avoids resin production through reacting hydroxymethyl phenols with a mercaptan in the absence of a catalyst. This patent does not realize that a highly effective antioxidant reaction product can be prepared through the simultaneous reaction of an alkylated phenol, formaldehyde and a primary or secondary mercaptan in the presence of an acid catalyst.
U.S. Pat. No. 3,903,173 discloses a process for the preparation of mono and dimethylene thioethers of dialkyl phenols wherein dialkyl phenols are reacted with formaldehyde and a mercaptan compound in an inert solvent in the presence of an alkaline compound such as sodium or potassium hydroxide. In a like manner, U.S. Pat. No. 4,304,904 uses at least one compound of lithium, magnesium, cobalt, nickel, copper, iron, chromium and aluminum as a catalyst to avoid the production of isomers, homologues and resins. These references fail to appreciate that under very critical reaction conditions, a highly desirable reaction product can be obtained that possesses excellent antioxidant properties.
Soviet Union Patent No. 1,150,257 discloses a lubricating/cooling liquid for metal processing which contains in weight percent, 1-3% chlorinated paraffin, 2-4% barium sulfonate, 2-3% dodecyl-thiomethyl-nonylphenol as a sulfur containing additive and mineral oil. The dodecyl-thiomethyl-nonylphenol is obtained by reacting dodecyl-mercaptan with formaldehyde and alkylphenol in benzene solution without a catalyst. The Soviet patent states that tests show the lubricating/cooling composition has improved lubricating properties, increased efficiency of metal working by 1.22 times, and wear resistance of cutting tools by 2.1 times, and reduced roughness of treated surface by 1.5 times. This reference does not suggest that an acid catalyzed reaction product would be useful as an antidegradant for oxidizable organic materials.
The search for new and better polymer and organic material stabilizers continues to command the attention of many skilled investigators; however, the prior art and literature on the subject does not disclose nor suggest that the acid catalyzed reaction of a phenol with formaldehyde and a mercaptan will result in a reaction product that is autosynergistic and which imparts outstanding oxidative resistance to the material into which it is incorporated. The novel reaction product of this invention and its process of preparation form the basis of the instant invention. The composition or mixture which results from the reaction disclosed herein is a superior stabilizer that overcomes some of the prior art problems of volatility, stabilizer extraction and the necessity of high levels of incorporation.